Vaillant VCW-sine 18 T3 W Pilot light

[Mike1501]

Hi,
I have an old Vaillant VCW-sine 18 T3 W (LPG) which seems to be generally still in fairly good condition. It has conked out a couple of times in recent years and has been repaired by a local LPG engineer with a few parts being replaced including the switch PCB, electronic PCB and flow switch/diverter valve. During the last couple of months it has developed a new fault - the pilot light going out. Some days it is fine; other days the pilot goes out repeatedly and has to be relit. I have monitored it on occasions and it seems to go out when the main burner switches off. It is then some time before the click of the thermo magnet occurs so I assume it is not the thermo-couple failing (that was replaced some years back anyway). It seems that the main burner going off causes the pilot to simply blow out. Any ideas why this is happening? And is there anything I can do about it or do I need to get an LPG engineer in again?
Thanks in advance for any advice.
Mike

 

[Beerlover]

Hi,
I have an old Vaillant VCW-sine 18 T3 W (LPG)

Any ideas why this is happening?

And is there anything I can do about it

I think you already know the answer - new boiler time. It must be over 25 years old!...................Dead horse.................Flogging...........HMMMMMM

 

[Mike1501]

No, these are the rolls royce of gas boilers - completely different league to the modern rubbish and almost as thermally efficient too. Probably another 25 years left in it.

 

[The831Bunny]

If the customer is happy: clean pilot, replace pilot injector and thermocouple. The proper Vaillant TCs 171125 fail about 2-3 years old on lpg, since they changed the design a while back. I've changed quite a few. You know if it's the 'newer' type as it's not a braided and the TC tip will be damaged & sooty!

Use a LPG registered Gas Safe engineer for these jobs.

 

[Mike1501]

Pilot has been cleaned, pilot injector and thermocouple replaced. Everything worked fine for a while and I thought the problem was solved. Now the pilot has started randomly blowing out again and when it does it is always when the main burner shuts down. I may be wrong but it seems to be turbulence in the combustion chamber that is causing it.
Mike

 

[DP]

it seems to go out when the main burner switches off

Might be the other way round. Pilot goes out and burner will therefore also drop out. Do you hear a click and then burner drops out? Is the burner downsizing as target temperature reached?

 

[Bunnyman]

I presume ur lpg man has checked flue outlet clear and the fins on ht exch are clean,as 831 said these stopped manufacture in 1988 and r deemed obsolete and delisted by Vaillant but r worth repairing if u can get the bits, I did a water valve on one this morning that British gas refused to mend! But urs sounds like flame lift is takin the pilot out so flue gas inlet pressure or fins locked on the main get ur reg man in

Untitled

• Bunnyman
• 26 Mar 2010
• 499

 

[Heini]

Pilot has been cleaned, pilot injector and thermocouple replaced. Everything worked fine for a while and I thought the problem was solved. Now the pilot has started randomly blowing out again and when it does it is always when the main burner shuts down. I may be wrong but it seems to be turbulence in the combustion chamber that is causing it.
Mike

Hello i'm owner of the same unit with the same problem.
I think it is surely not a problem of the thermo couple unit because i hear the click of the magnet after 30sec. (and this is o.k.)
It really looks like turbulence caused through the main burner.
When i then relit the pilot light it is ok, an the unit will heat fine.

Though it could not be a turbulence, cause the main burner then works fine going on and of in intervals.

After a pause of the unit, when room temperature is o.k.or in the morning, when i start to heat the error occurs again.

I don't want to replace the unit, though if you know how to fix this
error, please let me know.

Greetings from Duisburg